This part of site is an attempt to organize and add to the web resources for the Rover SD1
to form a cohesive and easily usable guide for those of us without easy access to
expert repair and/or advice. It is not offered in any way as a definitive source
and we take no responsibility for any errors that may exist.
Webmaster Rene Winters.
FULLY AUTOMATIC STARTING DEVICE (F.A.S.D.)|
In this section, we will examine the Zenith Fully Automatic Starting
Device F.A.S.D. fitted to the Rover SD1.
The FASD is controlled by coolant temperature. Coolant passes through the FASD
(on the right), and air enters at the top from the air cleaner.
Fuel is supplied from the carburettor float chamber.
Here we have removed the blue cover to see more of the mechanism. Inside the water
jacket '1' is a wax capsule, which expands against a spring inside tube '2' as coolant
temperature increases. This expansion pivots the drive lever '3' which in turn pushes
down the metering needle '4' and shut-off valve '5'. The air valve '6' is located in
the air intake.
In cross section, you can see the metering needle '4', the shut off valve '5' and the
air valve '6'. In the static position, the air valve is held closed by two springs '7'
and '8'. The area around the lower spring '8' is connected to manifold depression
via a delay valve '9'. The delay valve contains a bimetal strip '10' which in its
rest position holds a ball '11' on its seat.
During cranking, the air valve is held closed and fuel is drawn past the needle valve
into the outlet '12' to the engine.
As soon as the engine starts, current passes to the bimetal strip '10' in the delay valve.
The strip bends to allow the ball off its seat, and this in turn allows vacuum into the
area around the lower spring '8'. This vacuum acts down against the force of the spring,
and the air valve will open to weaken the mixture.
From there on, the warming coolant heats the wax capsule to move the linkage and
progressively push down the needle and shut-off valve. When the engine is fully warmed up,
the needle and valve are closed and the engine runs on the carburettor only.
Next the accelerator pump. It is necessary for the FASD to provide
additional mixture during acceleration. The pump is located in the base of the FASD,
and the plunger to it (arrowed), is moved down by the linkage from the wax capsule.
In this diagrammatic cross-section, you can see the components of the pump. The spring
loaded vacuum valve '2', links manifold depression '1' to the chamber '3'. The chamber
is split by a diaphragm '4', held down by a spring '5' and under which is fuel supplied
via inlet valve '6'.
It works like this. During high manifold depression conditions (seen on the left), the
diaphragm is raised against spring pressure. This draws in fuel under the diaphragm. When
the throttle is opened, (on the right), depression above the diaphragm decreases, allowing
the spring to push it down. Fuel is discharged through the exhaust valve to richen the
The items highlighted here cause the amount of fuel pumped to be progressively reduced as
the engine warms up. This control is achieved by the drive lever '7' which as we saw
earlier, is moved by the linkage from the wax capsule. As the engine warms up, the
drive lever will push down the plunger '8'. This restricts the upward movement of the
diaphragm and reduces the fuel delivery.
We have already mentioned the electrically controlled delay valve, so before we move
onto FASD checks and adjustments a word about the electrical circuit.
As we said before the delay valve '1' is a bimetal strip which holds a ball on its seat
when cold. It is connected to its control module '2' which is located behind the instrument
panel. The control module receives information from the coil '3' and the ignition
When the engine starts, as soon as 200 rpm is reached, current passes to the delay valve.
The bimetal strip then heats up to unseat the ball and allow vacuum under the air valve.
The current draw is 5 amps initially, dropping to 0.5 - 0.7 amps to hold the valve open.
Now testing the FASD. Check the tightness of all the hoses; always make sure there is
fuel being delivered and that coolant flows round the Wax capsule.
If the engine will not start from cold, check that the outlet pipe into the inlet
manifold is wet with fuel. If it is dry check the fuel supply then suspect a faulty FASD.
It may also be caused by a fault in the electrical circuit to the delay valve.
First check the voltage by connecting a voltmeter between the delay valve input terminal
and earth. During cranking there should be a zero reading, but as soon as the engine
starts, it should increase to battery voltage, 11-13V.
You must also check the current flowing. The amperage during starting is 5 amps, but
approximately 25 seconds after the engine has fired, it will drop to 0.5 - 0.7 amps as
you see here.
If the engine starts but runs rich when hot, you should suspect a faulty FASD unit.
To check, make sure the engine is at running temperature, connect a CO meter, and note
Disconnect and blank the manifold intake from the FASD unit, then note the CO reading
again. If it rises slightly, this is acceptable and the FASD unit is OK.
If the CO reading drops significantly, then the FASD unit is sticking open and should
There is one adjustment that can be made to the FASD, but this should only be done after
all other checks have been carried out. It involves altering the tension on the spring
opposing wax capsule expansion, thus changing the temperature at which the FASD operates.
To do it you will need a 1.5mm Allen key and a special test kit from Solex.
Starting with a cold engine, degrease the wax capsule water jacket and attach a
temperature sensitive label from the test kit.
Start the engine and allow it to idle, then position an 'air shut-off' indicator
over the FASD intake so it is held in place by vacuum.
Fit the Allen key in the end of the spring location and watch the temperature sensitive
label very closely as the engine warms up. Its segments will progressively change
colour from grey to black, and as soon as the 65° square starts to turn black,
turn the allen key clockwise until the air shut-off indicator falls off.
That completes the adjustment, but you must do it within 30 seconds. If you do not,
you will have to wait for at least one hour for the engine to cool, then start again
using a new temperature sensitive label.
Identification of the F.A.S.D. Units|
Isolated cases have been reported of incorrect FASD units being fitted in Service,
whilst they are identical externally, the vent fitted to each model differs internally.
They can be identified by a reference number stamped under the body casting on the side
furthest from the carburettor immediately below the blue plastic cover.
Specifications are as follows:
FASD Ref No.
BL Part No.